New cIts and cIam mutants of lambda gene cI will be isolated from E.coli Mut T (lambda ind-). These mutants will be mapped and characterized. Phage stocks containing a mutation that reduces transcriptions of cI will be constructed to test the hypothesis that transcription influences mismatch repair of amber mutants. A deletion that removes the recombination genes of lambda will be crossed into strains containing cI mutations that effect recombination. These strains will then be used in crosses to study the effect of rec genes of the host. Mutants in cI that significantly increase recombination or mismatch repair have been mapped by genetic crosses. Since the entire sequence of cI DNA is known, it is possible to assign mutants to a region of the sequence, but it would be desirable to know the precise sites of the mutations. Therefore, sequencing of selected mutants will be initiated.